Labour MP Diane Abbott has received enough nominations to stand for the party leadership in the UK.
The Hackney North and Stoke Newington MP will stand against former ministers David Miliband, his brother Ed, Andy Burnham and Ed Balls to take over from Gordon Brown.
She reached the necessary 33 nominations after John McDonnell announced earlier today that he was withdrawing from the race.
The Labour Party website revealed that Mr Burnham and Mr Balls also received 33 nominations, while David Miliband amassed 81 and Ed Miliband 63.
Voting will take place through September and the successful candidate will be announced before the start of the Labour Party's annual conference in Manchester on 25 September.
Mr Brown's successor will be chosen by a complicated electoral college system in which three sections - MPs and MEPs; affiliated organisations including trade unions; and party members - each wield one-third of the vote.
Voters will rank candidates in numerical order of preference on ballot papers, with a 'transferable eliminating' system used to redistribute votes until one contender has more than 50% support.
Labour is hoping that interest in the leadership contest will spark a surge in membership applications, with anyone joining the party before 8 September entitled to vote.
Acting leader of the Labour Party Harriet Harman, who nominated Ms Abbott, said: 'Over the next few months over four million people will have the chance to help shape Britain's progressive future by choosing the next leader of the Labour Party.
'This will be the biggest and most widespread election of any political party or any organisation in this country.
'The contest will be open, engaging and energising. It will be a chance to invite supporters to join the party to have a vote.'
Paul Kenny, general secretary of the GMB union, said he was 'very pleased' Ms Abbott would be on the ballot paper, adding: 'This will ensure there is going to be a much wider debate in the hustings.
'There are wide-ranging differences between the candidates on issues such as nuclear and privatisation and it is very important that these are aired.'
Meanwhile, the Liberal Democrats have elected Simon Hughes as the new deputy leader of the party.
Mr Hughes replaces Vince Cable who stepped down to focus on his job as business secretary in the coalition government.
The Bermondsey and Old Southwark MP was elected by Lib Dem colleagues in the House of Commons, defeating the only other contestant, Westmorland and Lonsdale MP Tim Farron. Both men are seen as part of the left-leaning wing of the party.
Mr Hughes, a veteran MP and one of the better known Lib Dem faces, was not given a cabinet post in the coalition deal.
He will face the difficult task of seeking to maintain a separate identity for the centre-left Lib Dems at a time when they are in government with the centre-right Conservatives.